Down's syndrome (DS) or trisomy 21 is the most frequent genetic cause of mental retardation. It occurs in about 1 in 800 to 1 in 1000 live births. Mental retardation and development of Alzheimer's disease (AD) by middle age are hallmarks of DS neuropathology. Previous studies demonstrated that DS neurons in culture exhibit elevated intracellular free radicals and lipid peroxidation leading to increased neuronal death. This increase in oxidative stress and neurodegeneration may contribute to mental retardation and the development of AD in DS patient. The goal of our research is to characterize the molecular mechanisms involved in neuronal oxidative stress and degeneration in DS. This project will study the role of Ets-2 and Cu/Zn superoxide dismutase (SOD-1) over- expression in DS neurodegeneration. The following hypotheses will be tested: 1. Over-expression of the transcription factor Ets-2 in DS neurons compromises neuronal viability by altering the expression of genes that control neuronal survival and death. More specifically, the possibility that Ets-2 down-regulates Bcl-2 and up-regulates Bax and p53 protein levels will be tested. 2. Increased activity of Cu/Zn superoxide dismutase (SOD- 1) may contribute to oxidative stress and DS neuronal degeneration. The research will focus on: 1) the functional analysis of Ets-2 and SOD-1 in DS and Ets-2 transgenic neurons in culture; and 2) the association of Ets- 2 and SOD-1 with neurodegenerative changes in the brains of DS and AD patients and Ets-2 transgenic mice. The specific aims are: 1: to determine the role of Ets-2 over-expression in DS neuronal degeneration in culture and in the brains of DS and AD patients. 2: To characterize the role of Ets-2 during normal neuronal development. 3: To determine the role of SOD-1 in DS neuronal degeneration. These experiments will provide valuable information towards understanding the molecular basis of neuronal dysfunction and death in DS and AD. In addition, the results of this investigation may identify new molecular targets for the design of neuroprotective therapies for the treatment of mental retardation and the prevention of AD in DS patients.